1. Field of the Invention
The present invention relates to an information carrier apparatus and an information carrier eccentricity correction method for correcting eccentricity of an information carrier based on an eccentricity direction and an eccentricity distance of an information carrier.
2. Description of the Related Art
A conventional information carrier apparatus (optical disc apparatus) described in Japanese Laid-Open Publication No. 52-80802 reproduces information (signal) recorded in an information carrier (optical disc) by: irradiating the information carrier with light having a relatively small light amount and detecting the light reflected by the information carrier. The information carrier apparatus also records information on an information carrier by adjusting the light amount of an optical beam in accordance with the information to be recorded on the information carrier and writing the information on a recording material layer included in the information carrier.
Generally, a reproduction-only information carrier has information represented by pits pre-recorded formed therein in a spiral manner.
Generally, a recording material layer capable of optically recording and reproducing information is deposited on a surface of a material of the information carrier capable of recording and reproduction. In the recording material layer, a track having a spiral concaved and convexed structure is formed. The information carrier capable of recording and reproduction is produced by depositing the recording material layer on the surface of the substrate by a technique such as, for example, vapor deposition.
In order to record information on an information carrier capable of recording and reproduction, or in order to reproduce information recorded on an information carrier capable of recording and reproduction, an information carrier apparatus performs focusing control and tracking control of a light collection lens included in the information carrier apparatus. The focusing control of the light collection lens is performed in a direction normal to the surface of the information carrier (hereinafter, referred to also as the “focusing direction”) such that the optical beam is always converged on the recording material layer. The tracking control of the light collection lens is performed in a radial direction of the surface of the information carrier (hereinafter, referred to also as the “tracking direction”) such that the optical beam is always on a prescribed track of the information carrier.
FIG. 16 shows a structure of a conventional information carrier apparatus 500 described in Japanese Laid-Open Publication No. 2001-160226.
The information carrier apparatus (optical disc apparatus) 500 includes an optical head 10, an FE (focusing error) signal generator 20, and an Fc filter 21. The optical head 10 includes a semiconductor laser device 11, a beam splitter 12, a light collection lens 13, a focusing actuator 14, a tracking actuator 15, and a light detector 16.
An information carrier 1 is mounted on the information carrier apparatus 500.
The semiconductor laser device 11 generates an optical beam. The optical beam passes through the beam splitter 12, and is converged on the information carrier 1 by the light collection lens 13. The optical beam is then reflected by the information carrier 1, again passes through the light collection lens 13, is reflected by the beam splitter 12, and is then directed to the light detector 16.
The light collection lens 13 is supported by an elastic member (not shown). When an electric current flows through the focusing actuator 14, the light collection lens 13 moves in the focusing direction by an electromagnetic force. When an electric current flows through the tracking actuator 15, the light collection lens 13 moves in the tracking direction by an electromagnetic force.
The light detector 16 detects a light amount of the light incident thereon on and sends a light amount signal representing the detected light amount to the FE signal generator 20.
The FE signal generator 20 generates an FE (focusing error) signal based on the light amount signal, and sends the FE signal to the focusing actuator 14 through the Fc filter 21. The FE signal represents the convergence state of the optical beam on the information carrier 1, more specifically, a deviation, in the focusing direction, between the focal point of the optical beam and a point on the information carrier 1 to which the optical beam is converged.
The Fc filter 21 performs phase compensation of the FE signal sent from the FE signal generator 20 in order to stably perform the focusing control of the light collection lens 13.
The focusing actuator 14 drives the light collection lens 13 in the focusing direction based on the FE signal sent from the FE signal generator 20 so as to focus the optical beam on an information face of the information carrier 1.
The information carrier apparatus 500 further includes a TKC signal generator 30, an OFTR signal generator 36, and a crossing detector 37.
The light detector 16 sends the light amount signal also to the TKC signal generator 30 and the OFTR signal generator 36.
The TKC signal generator 30 generates a signal indicating that the optical beam has crossed a certain track (hereinafter, referred to as a “TKC signal”) based on the light amount signal and sends the TKC signal to the crossing detector 37.
The OFTR signal generator 36 generates a signal indicating whether or not the optical beam is directed to the track (hereinafter, referred to as an “OFTR signal”) based on the light amount signal, and sends the OFTR signal to the crossing detector 37.
The crossing detector 37 detects the number of times that the optical beam has crossed the track based on the TKC signal and the OFTR signal, and generates a track crossing signal which indicates the number of times that the optical beam has crossed the track and also an eccentricity direction of the information carrier 1.
The TKC signal and the OFTR signal are offset in phase from each other by 90 degrees. Therefore, the crossing detector 37 can determine whether the optical beam is crossing the track toward an inner portion of the information carrier 1 or toward an outer portion of the information carrier 1. Accordingly, the track crossing signal generated by the crossing detector 37 includes information which indicates whether the optical beam is crossing the track toward an inner portion of the information carrier 1 or toward an outer portion of the information carrier 1, i.e., the information indicating eccentricity direction of the information carrier 1.
The information carrier apparatus 500 further includes a motor 34, an eccentricity driving generator 32, an eccentricity memory 33, and an eccentricity correction indicator 35.
The motor 34 rotates the information carrier 1 to generate a rotation phase signal which represents a rotation phase of the information carrier 1, and sends the rotation phase signal to the eccentricity driving generator 32 and the-eccentricity memory 33.
Based on the rotation phase signal, the eccentricity driving generator 32 obtains a track crossing signal sent from the crossing detector 37 for each rotation phase of the information carrier 1. The eccentricity driving generator 32 detects an eccentricity distance of the information carrier 1 corresponding to the rotation phase of the information carrier 1 based on the track crossing signal which indicates the number of times that the optical beam has crossed the track and also the eccentricity direction of the information carrier 1. The eccentricity driving generator 32 further generates a driving signal for correcting (or canceling) the eccentricity of the information carrier 1 based on the eccentricity direction and the eccentricity distance of the information carrier 1, and sends the driving signal to the eccentricity memory 33.
The eccentricity correction indicator 35 sends one of a signal indicating a state where the eccentricity is not corrected (no eccentricity correction state), a signal indicating a state where eccentricity correction is being learned (eccentricity correction learning state), and a signal indicating a state where the eccentricity is corrected (eccentricity correction state) to the eccentricity memory 33.
Only when the signal sent from the eccentricity correction indicator 35 indicates the eccentricity correction learning state, the eccentricity memory 33 obtains the driving signal sent from the eccentricity driving generator 32 and stores the driving signal in accordance with the rotation phase signal sent from the motor 34. Only when the signal sent from the eccentricity correction indicator 35 indicates the eccentricity correction state, the eccentricity memory 33 sends the driving signal stored therein to the tracking actuator 15 based on the rotation phase signal sent from the motor 34.
FIG. 17 shows a track crossing signal. In FIG. 17, the horizontal axis represents the rotation phase of the motor 34, and the vertical axis represents the number of times that the optical beam has crossed the track.
A track crossing signal is generated by the crossing detector 37 based on a TKC signal and an OFTR signal. Therefore, as shown in FIG. 17, the number of times that the optical beam has crossed the track is positive or negative based on the eccentricity direction of the information carrier 1.
The track pitch of an information carrier 1 is defined by the type of information carrier. The driving amount required by the tracking actuator 15 for moving the optical beam in the tracking direction by a prescribed distance is also defined by the type of information carrier apparatus. Accordingly, the eccentricity driving generator 32 can generate a driving signal for correcting the eccentricity of the information carrier 1 based on the track crossing signal.
While the motor 34 is performing one rotation, the eccentricity correction indicator 35 sends a signal indicating the eccentricity correction learning state to the eccentricity memory 33. Thus, the eccentricity memory 33 stores the driving signal for correcting the eccentricity of the information carrier 1 for each rotation phase of the motor 34.
Then, the eccentricity correction indicator 35 sends a signal indicating the eccentricity correction state to the eccentricity memory 33. Thus, the eccentricity memory 33 can send the driving signal for correcting the eccentricity of the information carrier 1 to the tracking actuator 15 for each rotation phase of the motor 34.
As described above with reference to FIGS. 16 and 17, the eccentricity direction is conventionally detected relying on the information recorded on the information carrier 1. For example, the TKC signal and the OFTR signal need to be detected in order to detect the eccentricity direction of the information carrier 1. In order to generate the OFTR signal, the OFTR signal generator 36 detects an amplitude of a signal representing the information recorded on the information carrier 1.
However, the information carrier 1, capable of recording information, has a portion in which no information is recorded. From such a portion, the eccentricity direction of the information carrier 1 cannot be detected. For example, an “amplitude of the signal indicating the information recorded in the information carrier 1” cannot be detected from such a portion, and therefore the OFTR signal cannot be generated. This makes it impossible to detect the eccentricity direction of the information carrier 1 based on the TKC signal and the OFTR signal.
FIG. 18 shows a track crossing signal which is generated by the crossing detector 37 when the OFTR signal cannot be detected. In FIG. 18, the horizontal axis represents the rotation phase of the motor 34, and the vertical axis represents the number of times that the optical beam has crossed the track.
Since the crossing detector 37 cannot detect the eccentricity direction of the information carrier 1, the number of times that the optical beam has crossed the track is shown to be simply increased. A driving signal for correcting eccentricity cannot be generated based on such a track crossing signal by the conventional technique.